Process of separating j-picoline



Patented cc. 1?, 1946 PROCESS OF SEPARATING 3-PICOLINE, 4-PICOLINE, AND2,6-LUTIDINE George Riethof, Mount Lebanon. Pa.

No Drawing. Application June 15, 1945, Serial No. 599,766

7 Claims. 1

This invention relates to a separation process; and more particularly itrelates to the separation of 3-picoline, -picoline, and 2,6-luticlinefrom one another.

One of the principal sources of these three compounds, 3-picoline,4-picoline, and 2,6-lutidine is the basic coal tar oils in which theycommonly occur associated with one another. These basic coal tar oilsmay be practically fractionated to produce certain cuts composedpredominately of a mixture of 3-picoline, -picoline and 2,6- lutidine.Hence, these materials are generally commercially obtained as a basicoil mixture boiling about 140-145" C. Since these compounds boil soclosely together, it is not commercially feasible to fractionate suchbasic oil mixtures into their separate components.

In my co-pending application, Serial No. 535,397, filed May 12, 1944,now Patent 2,383,016, granted August 21, 1945, I have disclosed thatsuch bases may be separated from each other and recovered by azeotropicdistillation utilizing a maximum boiling azeotrope and the process iscarried out by admixing a suitable quantity of phenol with the basicoils.

I have now discovered that formic acid may be employed to recover suchbases by a process of azeotropic distillation utilizing a maximumboiling point azeotrope. The use of such acid has certain advantagesover phenol.

The azeotrope formed with formic acid boils between 155 and 165 C. butby using these high temperatures, the formic acid decomposes rapidly andtherefore is not useable. I have found that formic acid becomes useableif the distillation is carried out under a sufficiently reducedpressure, e. g., 100 mm. to 200 mm. of mercury to thereby lower thetemperature of the maximum azeotrope so far, that none or very littledecomposition of formic acid occurs. Moreover, and quite unexpectedlythere is obtained a new result. That is, I find in all other maximumazeotropes such as those produced with phenol, acetic, propionic andisobutyric acids, the order of distilling over of the differentpicolines is first, 2-6 lutidine, 2nd, beta picoline and 3rd, gammapicoline. On the other hand, the formic acid azeotrope distills over ina different order namely, first beta-picoline, 2nd, gamma picoline, and3rd, 2-6 lutidine. Thus, the lowest boiling maximum azeotrope in thecase of the phenol and the allphatic acids becomes the highest boilingazeotrope by using formic acid. Since the most valuable component of thebasic oils is the beta picoin that the beta picoline can be obtainedsubstantlally pure and in a much simpler operation. There is noseparation to be carried out before the beta picoline comes over, as thefractional distillation of the maximum azeotrope has only to separatethe beta picoline from the gamma by an operation which in effect issimilar to a first containing oils into their separate components whichcan be easily operated with close control so as to yield commerciallypure products.

It is a still further object to provide a new separation process whichemploys the use or" maximum boiling azeoptropic mixtures.

Additional objects and the entire applicability of the present processwill become more apparent from the description of the invention givenhereinafter.

The objects are accomplished according to the process of my invention byadmixing the indicated basic oils with a suitable quantity of formicacid and distilling from this mass the maximum boiling azeotropes of thebasic components of the oil with the acid and separately collecting thevarious fractions,

The process of this invention is more fully illustrated in the followingexample, in which all parts are by weight unless otherwise specified.

Example A commercial mixture of 300 parts of a basic coal tar oilcontaining approximately 2,6.- lutidine, 3-picoline and 35% 4-picolineis charged into the still pot of a rather high eficiency fractionatingcolumn. To this basic oil is added 450 parts of formic acidconcentration) a ratio of acid to basic oil of about 4 to 3. Theacid/basic oil mixture is then subjected to fractional distillationthrough the column under a pressure of about 200 mm. of mercury and atemperature of about 110 to 125 C. or a pressure of about mm. of mercuryand a temperature of about 98 to C. A forerun of approximately 100 cc.of the total mixture, mostly of aqueous formic acid, is collected afterwhich the maximum boiling azeotropes of B-plcoline, s -picoline and2.6-lutidine distill over and are collected in that order.

In order to obtain 3-picoline of even higher purity the first cut or3-picoline/acid azeotrope is again fractionated through a similar columnand a fraction of 80% to 90% is collected. This middle fraction is thentreated with an excess of sodium hydroxide solution and the 3-picolineis distilled off.

The 2,6-lutidine and the 4-picoline fractions are treated in a similarfashion in order to obtain the substantially pure compounds.

The temperature range as given above as Well as the pressure ranges mayof course be varied but pressures and temperatures are utilized of anorder which is effective to prevent decomposition of the formic acid andassure that the fractions will distill over in the manner abovedescribed with the beta picoline constituting the first cut.

The ratio of formic acid to basic oils as illustrated in the aboveexample may be varied but preferably more acid by weight is employedthan the weight of the oil and it has been found best to employ anamount of the acid effective to form an azcotrope with all of the basicoil present, plus allowance for some decomposition of formic acid.

The composition of the basic oil being treated may be varied. However,this process is principally applicable to those basic oils which arecomposed predominately of 3-picoline, 4-picoline and 2,6-lutidine. Theratio by weight of these latter materials may be varied relative to oneanother.

Iclaim:

l. The process of separating a mixture predominately containing at leasttwo of the bases B-picoline, -picoline, and 2,6-lutidine which comprisesincluding in the mixture formic acid and fractionaiiy distilling themass under reduced pressure.

2. The process-of claim 1 wherein the distillates are acid azeotropes ofsaid bases.

3. The process of claim 1 wherein the distillate fractions boiling inthe range between substantially 98-125 C. under a pressure of about 200to 100 mm. of mercury are separately collected.

4. The process of claim 1 wherein the distillate fractions boiling inthe range between substantially 98-125 C. under a pressure of about 200to 100 mmv of mercury separately collected and redistilled.

5. The process of claim 1 wherein the distillate fractions boiling inthe range between substantially 98-125" C. under a pressure of about 200to 100 mm. of mercury are separately collected and redistilled andwherein the redistilled fractions are treated to recover thesubstantially pure base contained therein.

6. The process of separating a mixture containing at least two of thebases S-picoline, -plcoline and 2,6-lutidine which comprises includingin the mixture formic acid, fractionally distilling the mass, andthereafter recovering from the fractions the substantially pure casecontained therein, the fractional distillation being under reducedpressure and at a temperature effective to susbtantially preventdecomposition of the formic acid,

'7. The process of separating a mixture predominately containing atleast two of the bases 3-picoline, l-picoline, and 2,6-lutidine whichcomprises including in the mixture formic acid and fractionallydistilling the mass under re duced pressure, the fractions distillingover as 3-picoline, 4-picoline and 2,6-lutidine in the order named.

GEORGE RIETHOF'.

